Move canvas async work into app runtime

docs/modernization/debt.md

@@ -18,6 +18,21 @@ agent or engineer to remove them without reconstructing context from chat.
 
 ## Reductions
 
+- 2026-06-16: `DEBT-0003` was narrowed again. Canvas async
+  import/export/save/open background work now runs through an
+  `AppRuntime`-owned queue/worker in `src/app_runtime.h/.cpp`, and
+  `src/canvas.cpp` no longer defines a retained static canvas async worker;
+  broader app task ownership and retained runtime singleton reach remain.
+- 2026-06-16: `DEBT-0037` was narrowed again. `App::rec_loop()` in
+  `src/app.cpp` now routes its wait plus iteration plan/encode shell through a
+  local helper instead of carrying that orchestration inline; retained
+  recording loop control, readback call sites, and MP4 execution remain.
+- 2026-06-16: `DEBT-0036` was narrowed again. `NodeCanvas` grid-mode draw
+  callback setup now routes through
+  `make_legacy_canvas_draw_merge_grid_modes_draw(...)` in
+  `src/legacy_canvas_draw_merge_services.h` instead of keeping that callback
+  loop inline in `NodeCanvas::draw()`; broader canvas draw orchestration and
+  retained GL resource ownership remain.
 - 2026-06-16: `DEBT-0003` was narrowed again. Prepared-file background work
   now runs through an `AppRuntime`-owned queue/worker in
   `src/app_runtime.h/.cpp`, and `src/app_events.cpp` no longer defines a